1. Field of the Invention
The present invention relates generally to capacitors, and in particular to capacitors that are implemented within a semiconductor device.
2. Discussion of the Related Art
Conventional capacitors that are fabricated on semiconductor devices for storing charge are typically configured as metal-to-metal capacitors (MOMs). Referring to FIG. 1, the construction of a typical MOM 10 is illustrated. The MOM 10 includes two electrodes 12 that are formed on conductor layers 14 and 16 that are separated by a dielectric 18. A substrate 19 forms a base for the MOM 10. In addition to the device capacitance which is formed between the electrodes, there is also an undesirable parasitic capacitance that is formed between the substrate 19 and adjacent electrode. In many conventional devices, the parasitic capacitance may exceed 20% of the value of the capacitance between the electrodes of the capacitor. To increase the value of capacitance, generally either the plate area of the MOM is increased, or the dielectric thickness is decreased. Both of these options have drawbacks. Increasing the plate area causes a further undesirable increase in the parasitic capacitance, while reducing the dielectric thickness requires an extra process step that significantly increases the cost of the device. In addition, the matching characteristics of conventional semiconductor capacitors are deficient due to the non-symmetrical effect of external fields on adjacent capacitors.
The present invention provides a circuit and method for a fringing capacitor. The fringing capacitor includes at least two conductor layers spaced apart from each other. Each conductor layer includes at least two portions. The portions include odd ones alternating with even ones. Adjacent odd ones and even ones of the portions are spaced apart. The odd ones of the portions on a first one of the conductor layers are configured to substantially overlay the odd ones of the portions on an adjacent one of the conductor layers. The even ones of the portions on the first one of the conductor layers are configured to substantially overlay the even ones of the portions on the adjacent one of the conductor layers. The odd ones of the portions on the first one of the conductor layers are electrically coupled together and to the even ones of the portions on the adjacent one of the conductor layers, thereby defining a first electrode. The even ones of the portions on the first one of the conductor layers are electrically coupled together and to the odd ones of the portions on the adjacent one of the conductor layers, thereby defining a second electrode. A dielectric is interposed between the first and second electrodes. A guardband is spaced from the first and second electrodes.